Refractometer

ABSTRACT

The invention concerns a refractometer with a measuring prism on whose measuring surface a sample to be tested can be mounted, which sample can be illuminated by a light beam emitted by a source of light under a range of angles that includes the critical angle for total reflection, and with a receiver for receiving the reflected light, in which an optical device that decomposes the reflected light into a color spectrum is mounted in the path of the reflected light between the measuring surface and the receiver.

[0001] The invention concerns a refractometer with a measuring prism on whose measuring surface a sample to be tested can be mounted. The sample can be illuminated by a light beam emitted by a source of white light under a range of angles that includes the critical angle for total reflection. The refractometer also has a receiver for receiving the reflected light.

[0002] Refractometers are used to measure the index of refraction of solid, liquid, or gaseous substances. In total reflectometers, such as the Abbe refractometer, the critical angle of the total reflection is determined with the use of a measuring prism of known index of refraction, which is brought into optical contact with the substance to be tested.

[0003] These refractometers operate with white light, because the effect of dispersion can be compensated by rotation of two direct-vision prisms in the observation telescope.

[0004] The goal of the invention is to develop simple means of improving a refractometer, e.g., the Abbe refractometer, with respect to its ability to provide information about a substance to be tested.

[0005] In accordance with the invention, this goal is achieved by mounting an optical device that decomposes the reflected light into a color spectrum in the path of the reflected light between the measuring surface and the receiver.

[0006] In this solution to the problem, the dispersion that occurs is not eliminated again by an oppositely acting prism, but rather the color spectrum can be utilized to produce intensity curves for various wavelengths. If a two-dimensional diode array is used for detection, then the columns correspond to the various wavelengths, and the position of the light-dark border within the individual columns depends on the index of refraction at the given wavelength. The index of refraction can thus be represented as a function of the wavelength.

[0007] The use of the CCD array provides still another advantage.

[0008] Due to the total reflection, a number of rows will always be light, namely, those on which the totally reflected light is incident. However, this light now contains information about the absorption of the sample, which likewise can be analyzed.

[0009] The drawings show the design of the refractometer in simplified form with the source of white light 1, the measuring prism 2, and the sample 3 on the measuring surface of the prism. The systems of lenses 4 are merely indicated in the drawing. An optical device 6 that produces a spectrum, e.g., a grating or a direct-vision prism, is arranged between the measuring prism and the receiver 5. 

1. Refractometer with a measuring prism on whose measuring surface a sample to be tested can be mounted, which sample can be illuminated by a light beam emitted by a source of white light under a range of angles that includes the critical angle for total reflection, and with a receiver for receiving the reflected light, characterized by the fact that an optical device that decomposes the reflected light into a color spectrum is mounted in the path of the reflected light between the measuring surface and the receiver.
 2. Refractometer is accordance with claim 1, characterized by the fact that the optical device is a grating.
 3. Refractometer in accordance with claim 1, characterized by the fact that the optical device is a dispersion prism.
 4. Refractometer in accordance with any of the preceding claims, characterized by the fact that the receiver is two-dimensional CCD array.
 5. Refractometer in accordance with claim 1, characterized by the fact that the receiver is a one-dimensional CCD row, which is moved by stepper motors parallel to the columns (along the color bands). In this way, although the measurement can only be made sequentially with respect to time, it has the advantage that a longer row of correspondingly greater resolution for the index of refraction and wavelength determination is provided. 